Modified Unipolar Return Pulsed Field Ablation in Ventricular Myocardium

Abstract

Background: Various pulsed field ablation (PFA) parameters have been proposed to improve lesion depth. This study evaluated a modified unipolar return PFA system to create deep lesions in healthy and infarcted ventricular myocardia.

Methods: Numerical modeling was used to compare a modified unipolar return PFA system configuration with a conventional unipolar return (skin patch). We then performed ablation in 14 swine (5 with chronic myocardial infarction and 9 healthy). PFA lesions were created in the left ventricle using a focal catheter (4-mm tip) with a return electrode positioned in the inferior vena cava (biphasic, microsecond pulses of 1300 and 1500 V, 1-16 trains). Electroanatomical mapping guided ablation and lesion localization on magnetic resonance imaging were performed 48 hours post-ablation in the infarcted group and at 1 day, 7 days, and 6 weeks post-ablation in the healthy group.

Results: Numerical modeling demonstrated that the modified unipolar return PFA system produced deeper lesions with reduced variability compared with the skin patch. In healthy pigs (n=35 lesions), depths of 6.8±1.8 mm and widths of 11.5±4.7 mm were achieved with 8 pulse trains. Depths of 8.2±2.8 mm and widths of 14.0±4.7 mm were achieved with 16 trains. The maximum lesion depths were 8.8 and 11.6 mm for 8 and 16 trains, respectively. In the infarcted cohort (n=22 lesions), all lesions applied to scar tissue penetrated through fibrotic regions, with epicardial involvement observed in 57% of lesions.

Conclusions: The modified unipolar return PFA system effectively creates large lesions and can achieve transmurality in healthy and infarcted animals. Compared with conventional unipolar, it may offer greater lesion depth, width, and consistency.

Keywords: atrial fibrillation; catheter ablation; heart ventricles; pulmonary veins; tachycardia, ventricular.

Figure 1.

Study setup and cardiac magnetic resonance imaging (cMRI) reconstruction. Left, Fluoroscopy image with a return decapolar catheter in the inferior vena cava, a reference decapolar catheter in the coronary sinus, and the focal pulsed field ablation (PFA) catheter in the left ventricle with retrograde aortic approach. Right, cMRI reconstruction of the left ventricle post-ablation including the PFA lesions.

Figure 2.

Numerical model: modified unipolar return pulsed field ablation (PFA) system (MURAL) vs standard unipolar. Numerical modeling results for PFA lesion depth (1500 V, 16-train protocol) and impedance for the standard unipolar (skin patch) and MURAL (inferior vena cava [IVC] catheter) return electrode configuration. A, Predicted lesion depth across the 13 left ventricle (LV) segments for 50- and 100-kg swine for the 2 return electrode configurations and standard positions (skin patch in the lumbar region and IVC catheter positioned as in the experiments). Boxplots for (B) lesion depth and (C) impedance for the 2 return electrode configurations, different positions, and different animal sizes (50 and 100 kg). Each boxplot represents calculated values for ablation catheter positions across the 13 different LV segments for the given return electrode configuration, position, and swine size. Whiskers indicate the minimum and maximum values of the data.

Figure 3.

Lesion size at different energy doses. Left, Distribution of width and depth at different voltages and numbers of repetitions. Boxplots represent the median and interquartile range, and the whiskers indicate the minimum and maximum values of the data. Right, Lesion shape with increasing number of repetitions. The maximum width is subendocardial for high-energy dose lesions, with a similar shape and size compared with 4 trains.

Figure 4.

Cardiac magnetic resonance imaging and histology 6 weeks after ablation with 1500-V 16 trains. Top left, Three-dimensional late gadolinium enhancement image at 6 weeks showing a posteroseptal lesion. Top right, Gross pathology. Bottom, Masson trichrome 6 weeks post-ablation with well-demarcated replacement fibrosis sparing vessels.

Figure 5.

Lesion size over time. Lesion width remained stable over time for most energy doses. Lesion depth did change significantly between the time points although the difference in depth was more pronounced between 24 hours and 7 days. Boxplots represent the median and interquartile range, and the whiskers indicate the minimum and maximum values of the data.

Figure 6.

Histology of pulsed field ablation lesion in myocardial scar 24 hours post-procedure. Pulsed field ablation penetrated through dense scar, reaching epicardial spared tissue and islands of preserved myocardium within the infarcted area.